1. Field of the Invention
The present invention relates to a solid-state imaging device including: a semiconductor substrate, a plurality of photoelectric conversion elements that are arranged on the semiconductor substrate, and color filter layers of a plurality of colors that are formed in a predetermined pattern above the plurality of photoelectric conversion elements, and a method of manufacturing the same.
2. Description of Related Art
In a color solid-state imaging device, for the formation of color images, color filter layers (dye layers) corresponding respectively to photoelectric conversion elements are formed in accordance with a predetermined arrangement (see, for example, JP11-150252 A). Hereinafter, the structure of a conventional solid-state imaging device having color filter layers will be described briefly.
Generally, for a single-plate color solid-state imaging device in which a color filter of three primary colors is used with respect to one solid-state imaging device for the formation of color images, a color filter of a Bayer arrangement as shown in FIG. 9 often is used. In a color filter layer 20 shown in the figure, green color filter layers 20G (without hatching) are arranged so as to form a checkered pattern, and gaps in the checkered pattern are occupied alternately by blue color filter layers 20B (with vertical hatching) and red color filter layers 20R (with horizontal hatching). That is, on one line (A-A″ line), the green and blue color filter layers are arrayed in an alternate and repeated manner, while on a line adjacent thereto (B-B″ line), the red and green color filter layers are arrayed in an alternate and repeated manner.
FIG. 10 is a diagram schematically showing a cross section of the conventional solid-state imaging device along the A-A″ line of FIG. 9. The following briefly describes a cross-sectional structure of this solid-state imaging device. That is, a P-type well layer 12 is formed on a N-type semiconductor substrate 11, and on the P-type well layer 12, a plurality of photoelectric conversion elements 13 that perform photoelectric conversion are formed as N-type semiconductor layers. Further, a gate insulation film 14 that covers the P-well layer 12 and the photoelectric conversion elements 13 is formed, and a transfer electrode 15 that performs signal transfer is formed in a position corresponding to a portion between the photoelectric conversion elements 13.
Moreover, an interlayer insulation film 16 is formed so as to cover the transfer electrode 15, and a light-blocking film 17 is formed so as to cover the interlayer insulation film 16. The light-blocking film 17 prevents the incidence of undesired light on the transfer electrode 15. Further, a surface protection film 18 is formed so as to cover the gate insulation film 14, the light-blocking films 17 and the like, and a first transparent planarization film 19a that fills each concave portion on a surface of the surface protection film 18 is formed. A second transparent planarization film 19b made of a thermosetting transparent resin is formed on respective surfaces of the surface protection film 18 and the first transparent planarization films 19a, which now form a planarized surface, and the color filter layer 20 is formed on the second transparent planarization film 19b. The second transparent planarization film 19b improves an adhesion property of the color filter layer 20 and also reduces a development residue. A third transparent planarization film 19c is formed on the color filter layer 20, and on the third transparent planarization film 19c, a microlens 21 is formed with respect to each pixel. The microlens 21 enhances the light-condensing efficiency of each pixel with respect to a corresponding one of the photoelectric conversion elements 13.
The color filter layer 20 is an aggregation of color filter layers, each having a predetermined dye (red, green or blue) with respect to each pixel. In FIG. 10 showing the cross section along the A-A″ line of FIG. 9, the blue color filter layers 20B and the green color filter layers 20G are formed alternately. In the conventional solid-state imaging device described in JP11-150252 A, each of the green color filter layers 20G being large in number is formed so as to have an area larger than an area of the blue color filter layer 20B. Moreover, an edge portion of the green color filter layer 20G (an interface between the green color filter layer 20G and another color filter layer) is formed diagonally so that an area in which the green color filter layers 20G are in contact with the second transparent planarization film 19b is increased further. This makes the color filter layer 20 resistant to peeling.
In the cross section shown in FIG. 10, compared with a pixel size, the size of the green color filter layer 20G is increased, and the size of the blue color filter layer 20B adjacent thereto is decreased accordingly. Therefore, in the case where blue light is incident on a boundary portion between a green pixel and a blue pixel as shown in FIG. 10, the blue light is absorbed in the green color filter layer 20G, and thus an amount of light reflected diffusely on a surface of the light-blocking film 17 or the like is decreased. As a result, the amount of light received by the photoelectric conversion element 13G positioned under the green color filter layer 20G interposed between the blue color filter layers 20B hardly changes.
FIG. 11 is a diagram schematically showing a cross section of the conventional solid-state imaging device along the B-B″ line of FIG. 9. This cross-sectional view is different from the cross-sectional view shown in FIG. 10 only in the configuration of the color filter layer 20. That is, in this cross section, the green color filter layers 20G and the red color filter layers 20R are formed alternately.
Also in the cross section shown in FIG. 11, compared with the pixel size, the size of the green color filter layer 20G is increased, and the size of the red color filter layer 20R adjacent thereto is decreased accordingly. Therefore, in the case where blue light is incident, the blue light is absorbed in the green color filter layer 20G, and thus an amount of light reflected diffusely on the surface of the light-blocking film 17 or the like is decreased. As a result, the amount of light received by the photoelectric conversion element 13G under the green color filter layer 20G interposed between the red color filter layers 20R hardly changes.
That is, as shown in FIGS. 10 and 11, in the case where, compared with the pixel size, the size of the green color filter layer 20G is increased, and the respective sizes of the blue color filter layer 20B and the red color filter layer 20R that are adjacent thereto are decreased accordingly, no difference is produced between the amount of light received by the photoelectric conversion element 13G of a green pixel interposed between the blue color filter layers 20B and the amount of light received by the photoelectric conversion element 13G of a green pixel interposed between the red color filter layers 20R.
The same holds true for the case where red light is incident. The red light is absorbed in the green color filter layer 20G. Therefore, the amount of light received by the photoelectric conversion element 13G under the green color filter layer 20G interposed between the blue color filter layers 20B hardly changes, and neither does the amount of light received by the photoelectric conversion element 13G under the green color filter layer 20G interposed between the red color filter layers 20R. Thus, no difference is produced between these amounts.
As described above, line shading that occurs due to a difference in green sensitivity between on the A-A″ line and on the B-B″ line of FIG. 9 is suppressed by a method in which the green color filter layers are formed in a size larger than a pixel size. Further, JP 5-110044 A describes a structure in which a black filter portion is formed on a portion between each pair of adjacent pixels to block light incidence.
However, the conventional solid-state imaging device having color filter layers that are formed so that green color filter layers have a size larger than a pixel size as described above presents the following problems.
Firstly, in the case where oblique light is incident, since the green color filter layers are formed in an increased size, light that has been transmitted through the green color filter layer is incident on the blue color filter layer or the red color filter layer that is adjacent thereto to cause color mixture, and thus high-definition images cannot be obtained.
Secondly, when oblique light is incident in the cross section on the A-A″ line of FIG. 9 as shown in FIG. 12, after being transmitted through the green color filter layer 20G, this light is incident on the photoelectric conversion element 13B of a blue pixel under the blue color filter layer 20B adjacent to the green color filter layer 20G. As a result, with respect to a blue spectral characteristic, part of a long wavelength component in green light is added, resulting in an increase in blue sensitivity. Similarly, when oblique light is incident in the cross section on the B-B″ line of FIG. 9 as shown in FIG. 13, after being transmitted through the green color filter layer 20G, this light is incident on the photoelectric conversion element 13R of a red pixel under the red color filter layer 20R adjacent to the green color filter layer 20G. As a result, with respect to a red spectral characteristic, part of a component in the green light is added, resulting in an increase in red sensitivity.
Thirdly, in the case where line shading is suppressed by the method in which green color filter layers are formed in a size larger than a pixel size (resizing), it is difficult to optimize an amount of the resizing so as to correspond to a solid-state imaging device. That is, it is extremely difficult to determine a resizing amount that allows the influence of oblique light to be reduced and is effective in suppressing line shading.
Furthermore, with a color resist forming a color filter layer coated in an increased thickness, in an exposure process step in a photolithography technique, i-rays are absorbed by the color resist and hardly reach a deep portion. Because of this, only an insufficient degree of photopolymerization occurs in the deep portion, so that film peeling becomes more likely to occur. Meanwhile, in order to obtain a desired spectral characteristic, a color resist is required to be coated in a somewhat large thickness. Moreover, it is extremely difficult to obtain pigment particles in the form of fine particles, and even if such particles are obtained successfully, it is inevitable that an increase in secondary particle diameter occurs as a result of a dispersion treatment, which hinders the reduction of thickness for a pigment-dispersed color resist.
Furthermore, in the conventional solid-state imaging device, as previously described, each color filter layer has an edge portion that is not perpendicular to but oblique to a substrate. That is, green color filter layers that are formed first have a cross section of a trapezoidal shape (upper base dimension<lower base dimension). Color filter layers (of, for example, blue and red colors) that are formed second and third are formed so as to fill gaps in a pattern of the color filter layers that are formed first and thus have a cross section of a trapezoidal shape having an upper base dimension larger than its lower base dimension. As a result, as shown in FIGS. 12 and 13, it is more likely that oblique incident light is transmitted through an edge portion of a color filter layer of an adjacent pixel. Because of this, a desired spectral characteristic cannot be obtained, and color mixture occurs.
Moreover, there also is a problem that the use of microscopic pixels leads to deterioration of an alignment margin in a cross-sectional shape of a color filter layer. When an alignment deviation occurs, due to incident light being transmitted through a peripheral portion of a color filter layer of an adjacent pixel, a greater degree of color mixture occurs, and thus a desired spectral characteristic cannot be obtained.
In addition, when green color filter layers are formed in a checkered pattern in a color filter of the Bayer arrangement, if a color filter resist material having poor resolution is used, the shape of an edge portion at a peripheral portion of each color filter layer may be deteriorated, and in a worst case, the edge portion of the color filter layer may be distorted. Such a distortion of the edge portion occurs in an irregular manner and thus is difficult to prevent through designing of a mask.